The present invention is concerned with a novel process for the manufacture of cyclohexene derivatives. More particularly, the invention is concerned with a process for the manufacture of cyclohexene derivatives which are suitable as intermediates for the manufacture of rhodoxanthin or zeaxanthin, as well as a process for the manufacture of rhodoxanthin or of zeaxanthin itself.
The term zeaxanthin used in this Specification means (3RS,3'RS)-zeaxanthin.
Rhodoxanthin is a naturally occurring carotenoid which can be used, inter alia, as a foodstuff colouring substance. Zeaxanthin, the (3R,3'R)-antipode of which occurs in nature, can also be used as a foodstuff colouring substance (e.g. for egg yolk pigmentation).
Hitherto known syntheses for the manufacture of these two carotenoids require about 10 to 18 steps. Thus, for example, known multistep processes for producing these compounds are described in the following papers:
H. Mayer et. al. Helv. Chim Acta 50, 1606 (1967); PA1 J. S. Surmatis et al. Helv. Chim Acta 53, 974 (1970) PA1 J. D. Surmatis et. al. J. Org. Chem 35 1053 (1970) (describes a 15 to 16 step synthesis of rhodoxanthin) PA1 P. Karrer et al. Helv Chim Acta 18 477 (1935) (describes the conversion of rhodoxathin to racemic zeaxanthin); and PA1 R. Kuhn et al. Berichte 66 1319, (1933) (describes the oxidation of dihydrohodoxanthin to rhodoxathin).